# File lib/mailfactory.rb, line 65
  def add_header(header, value)
    value = quoted_printable_with_instruction(value, @charset) if header == 'subject'
    value = quote_address_if_necessary(value, @charset) if %w[from to cc bcc reply-to].include?(header.downcase)
    @headers << "#{header}: #{value}"
  end